System streams defined by the MPEG2 standard (ISO/IEC 13818-1) are used to compress video at a low bit rate. The following three types are defined as this system stream: program stream; transport stream; and PES stream.
On the other hand, optical disks such as phase-change optical disk (e.g., DVD-RAM or MVDISC) or magneto-optical disks (MO) have attracted attention as a recording medium replacing a magnetic tape. For example, VIDEO RECORDING standard (DVD Specifications for Rewritable/Re-recordable Discs Part 3 VIDEO RECORDING Version 1.0 September 1999) is one standard under which video is recorded on a DVD-RAM. This standard is used to record/reproduce video files constituted by program streams under the MPEG2 standard with respect to a DVD-RAM disk. Hereinafter, conventional techniques including the technique of the VIDEO RECORDING standard will be described by explaining the case where video files constituted by MPEG2 transport streams are recoded/reproduced with respect to a phase-change disk (hereinafter, referred to simply as “optical disk” as long as it is not confusing) instead. In the description below, video is compressed under the MPEG2 of ISO/IEC 13818-1, and audio is compressed under the MPEG2-AAC (Advanced Audio Coding) of ISO/IEC 13818-7.
FIG. 16 shows a configuration diagram of a conventional audio/video information recording/reproducing device using a phase-change optical disk. When recording video signals and audio signals, signals input from a video signal input portion 100 and an audio signal input portion 102 are compressed in a video compressing portion 101 and an audio compressing portion 103, respectively. Then, dummy packets generated by a dummy packet generating portion 105 for post-recording are mixed with the compressed results in a transport stream assembling portion 104 to produce transport streams. Then, the transport streams are written in a phase-change optical disk 131 via a buffer memory 154, a recording portion 120 and a pick-up 130.
When reproducing video signals and audio signals, the transport streams picked up by the pick-up 130 and passed through a reproducing portion 121 and the buffer memory 154 are separated into video signals and audio signals in a transport stream disassembling portion 115 and are output to a video display portion 110 and an audio output portion 112 via a video expanding portion 111 and a first audio expanding portion 113, respectively. A second audio expanding portion 114 is used to reproduce back audio (described later) when the back audio is recorded in the transport streams.
When recording video signals and audio signals, a recoding control portion 151 controls the recording portion 120, a continuous data area detecting portion 150 and a logical block managing portion 141 and performs recording. In this case, the continuous data area detecting portion 150 checks the use status of the sectors managed by the logical block managing portion 141 in response to an instruction of the recording control portion 151 and detects vacant areas that physically are continuous.
When reproducing video signals and audio signals, a reproducing control portion 140 controls a reproducing portion 121 and the recording portion 120 and performs reproduction. A recording control portion 152 for post recording and a reproducing control portion 153 for post-recording are started up at the time of post-recording, which will be described later.
It should be noted that “recording of video signals and audio signals” is referred to as “recording of motion picture signals” in the following. Similarly, “recording of video and audio” is referred to as “recording of motion pictures”.
FIG. 17 shows a recording format for recording video in real-time in the phase-change optical disk 131. The phase-change optical disk 131 is constituted by 2 kbyte sectors, and 16 sectors constitute one logical block (32 kbytes). An error correction code is provided with every logical block for recording in the phase-change disk 131. Furthermore, logical blocks that physically are continuous at least for a specific time (e.g., 0.86 seconds as described later) in terms of the maximum recording/reproducing rate are taken as one continuous data area. In this area, video object units (hereinafter, referred to as “VOBU”) having a reproduction time (display time) of 0.4 to 1 second and constituted by MPEG transport streams are recorded sequentially. One VOBU contains video and audio compressed data that entirely can be decoded without additional data in principle. In other words, video and audio compressed data are complete within one VOBU.
One VOBU is constituted by transport packets with 188 bytes each, which are in a subordinate level of the MPEG transport stream. The transport packet is constituted by the following three types of transports packets: a video transport packet (V_TSP) in which video compressed data are stored, an audio transport packet (A_TSP) in which audio compressed data are stored, and a dummy audio transport packet (D_TSP). One VOBU contains all of V_TSP, A_TSP and D_TSP in a corresponding time. The data size of one VOBU is varied in the range up to the maximum recording/reproducing rate, if the bit rate of video signals is variable. On the other hand, if the bit rate of video signals is fixed, the data size of the VOBU is substantially constant.
FIG. 18 is a diagram showing the detail of V_TSP, A_TSP and D_TSP. The V_TSP includes a transport packet header and video data, the A_TSP includes a transport packet header and audio data, and the D_TSP includes a transport packet header and dummy data for back audio. The difference between the V_TSP, the A_TSP, and the D_TSP is identified with the PID (packet ID) in the transport packet headers. For example, as shown in FIG. 18, the V_TSP, the A_TSP, and the D_TSP are identified by assigning PID=“0x0020” to the V_TSP, PID=“0x0021” to the A_TSP, and PID=“0x0022” to the D_TSP.
The continuous data area detecting portion 150 of the audio/video information recording/reproducing device shown in FIG. 16 redetects the next continuous data area at the time when the remaining area of one continuous data area becomes small. Then, when one continuous data area is filled up, writing is performed in the next continuous data area.
FIG. 19 shows the state in which the contents recorded on an optical disk are managed by a UDF (Universal Disk Format) file system. In this example, one MPEG transport stream is recorded as a file “MOVIE. MPG” by one ON operation and one OFF operation with a recording start button. The name and the file entry position of the file are managed by a FID (File Identifier Descriptor). Furthermore, one file and three continuous data areas a, b and c constituting this file are managed with allocation descriptors in the file entry. The following explains how the continuous data area has come to be divided into three portions. The structure of each allocation descriptor is composed of an extent length and an extent position as shown in FIG. 20.
When the recording control portion 151 finds a defective logical block while recording data in the continuous data area a, the recording control portion 151 skips the defective logical block and continues writing from the head of the continuous data area b. When the recording control portion 151 is about to arrive in an area where a PC file is recorded while recording data in the continuous data area b, the recording control portion 151 continues writing from the head of the continuous data area c. As a result, the file “MOVIE. MPG” is constituted by the three continuous data areas a, b, and c.
FIG. 21 shows the outline of the operation at the time of reproduction of a file. For reproduction, the reproducing control portion 140 performs simultaneously an operation of reading data from the optical disk 131 to the buffer memory 154 and an operation of reproducing data by data transfer from the buffer memory 154 to the transport stream disassembling portion 115. In this case, the data reading rate Vr is set to be higher than the data reproducing rate Vo so as to prevent data to be reproduced from not being present in the buffer memory 154 (underflow). Therefore, when continuous data reading and continuous data reproduction are performed constantly, surplus data to be reproduced can be held in an amount corresponding to the difference in the rate between the data reproducing rate Vo and the data reading rate Vr. Reproduction can be performed continuously by using this surplus data that can be held as reproduction data when data reading is interrupted by the jumping of the pick-up 130.
More specifically, when the data reading rate Vr is 24 Mbps, the data reproducing rate Vo is 10 Mbps, and the maximum movement time of the pick-up 130 is 0.5 seconds, surplus reproduction data of 5 M bits are necessary during pick-up movement. In order to obtain such surplus reproduction data, continuous reading for 0.36 seconds is necessary. In other words, it is necessary to perform continuous reading for a period of time obtained by dividing 5 M bits by the difference between the data reading rate, which is 24 Mbps, and the data reproducing rate, which is 10 Mbps.
Here, reproduction data of 8.6 M bits, that is, reproduction data for 0.86 seconds in terms of a reproducing rate of 10 Mbps is read during continuous reading of 0.36 seconds. Therefore, ensuring a continuous data area for 0.86 seconds or more to record motion pictures at up to 10 Mbps makes it possible to guarantee continuous data reproduction.
The maximum movement time of the pick-up 130 refers to a period of time that is required for a disk to move between the innermost circumference and the outermost circumference. This period of time includes rotational latency.
Several defective logical blocks may be present in the middle of the continuous data area. In this case, however, it is necessary to increase the continuous data area to an area slightly larger than the area for 0.86 seconds in view of a reading time necessary for reading the defective logical blocks for reproduction.
One of the functions commonly provided in a consumer movie is post-recording. Post-recording is a function of dubbing audio corresponding to video that is recorded once (hereinafter, referred to as “front audio”) to newly recorded audio (hereinafter, referred to as “back audio”).
The post-recording generally is constituted by the following three steps. In the first step, video is recorded in a recording mode that allows post-recording (hereinafter, referred to as “post-recording mode recording”). In the second step, back audio is recorded in synchronization with the recorded video while watching the recorded video (hereinafter, referred to as “post-recording recording”). In the third step, the video and the back audio in the second step are reproduced in synchronization (hereinafter, referred to as “post-recording reproduction”). These steps attain dubbing.
In the first step, the recording control portion 152 for post-recording records a MPEG transport stream including V_TSP, A_TSP, and D_TSP. In the second step, the recording control portion 152 for post-recording replaces D_TSP by A_TSP for back audio and records the A_TSP for back audio in the optical disk 131. In the third step, the reproducing control portion 153 for post-recording controls such that A_TSP for front audio, A_TSP for back audio and V_TSP are delivered to the transport stream disassembling portion 115. Thus, dubbing is attained.
A file including video and audio to be recorded during post-recording recording is referred to as a “motion picture file” in the following.
When there is no need for post-recording, a motion picture file that does not include D_TSP and is constituted by A_TSP and V_TSP is recorded.
When the reproducing control portion 140 reproduces a motion picture file that is recorded in the post-recording mode, D_TSP is not delivered to the transport stream disassembling portion 115, and A_TSP and V_TSP are delivered.
When recording back audio while watching video during post-recording recording, it is necessary to perform a process for reproducing video and a process for re-recording video including back audio at the same time. More specifically, the reproducing control portion 153 for post-recording stores a stream to be reproduced on the buffer, replaces D_TSP in the stream by A_TSP for back audio, and writes it back on the disk. That is to say, it is necessary to perform simultaneously continuous reproduction at the rate at which the video is recorded and continuous recording at the same rate. In order to realize this concurrent recording/reproducing process, it is necessary to realize a high transfer rate and a high-speed seek time, which requires an expensive disk drive.